Side effects of ultrasound during pregnancy

Ultrasound is used by doctors to take image of the growing fetus. The usual ultrasound prenatal test can help to confirm pregnancy, multiple pregnancies, gender of baby, detect ectopic pregnancy, detect abnormality in the growth of the fetus, verify position of the fetus and has many other useful functions. Doppler ultrasound can help to check blood flow rate

Although it has some many benefits, its uses may also have adverse side effect.

Different types of ultrasound

Transvaginal ultrasound:  This is usually done in the first trimester of pregnancy. This kind of ultrasound is done through the vagina.

Transabdominal ultrasound: This is usually done in the second or third trimester of pregnancy. Gynecologist will apply a thin layer of gel on the belly. The gel helps the sound waves move more easily so that a better picture of the fetus can be obtained.

In Singapore, this test may take about 40 minutes to complete.

Doppler ultrasound: This is a special type of ultrasound which creates image of blood flow through vessel.

3-D ultrasound: A 3-D ultrasound takes thousands of pictures at once. It makes a 3-D image of the growing fetus to confirm that his or her organs are developing normally. 3-D ultrasound can also help to check for problems in the uterus.

4-D ultrasound: This is like a 3-D ultrasound, but it also shows baby’s movements in a video.

How ultrasound can cause adverse effect?

There are two major ways in which ultrasound can cause adverse effect: heat and acoustic streaming.

Heat

The sonar beam can cause heating in the tissues beings scanned. Ultrasound can cause temperature of the tissue to be increased by about 2 degree Celcius. However, this should be safe as increase in body temperature of 4 degree is presumed to be safe during normal pregnancy.

Doppler ultrasound, which uses continuous waves, has been shown to cause more significant heating – especially in the baby’s developing brain.

Acoustic streaming

Acoustic streaming is a steady flow in fluid drived by the ultrasound wave. This phenomenon adds stress to a cell. Research suggests that this additional stress may change cell permeability and have adverse effects on both early and late prenatal and postnatal development.

Side effect of ultrasound during pregnancy               

Lower birth weight

Published in 1993, a study involving about 3,000 pregnant women showed that 1415 women who went for five times (week 18, 24, 28, 34, 38) ultrasound imaging or Doppler flow studies during pregnancy were much more likely to give birth to child who were underweight as compared to 1419 women who only received one ultrasound at week 18. This showed that frequent exposure to ultrasound may have influenced fetal growth. 

Neurological problem

In a study involving mice with result published in Proceedings of the National Academy of Science, a group of researchers had confirmed that the ultrasound damaged mouse brain.

Although only mice were involved, the result still showed that it was likely that the ultrasound can have an adverse effect on the brain development of the fetus as the method of development in mouse brains is exactly the same in all mammals. If ultrasound has an adverse effect on mouse brains, then it is very likely that it also has the same effect on human brains.

Autism

Some neurologists also suspect that ultrasound exposure may be a factor that contributes towards to autism. Manuel Casanova M.D., a neurologist at the University of Louisville in Kentucky suspected that ultrasound exposure was an environmental factor directly contributing to the exponential rise in autism.

Recommendation on use of ultrasound during pregnancy

1. Using ultrasound only when a problem is suspected. Do not use ultrasound to determine the gender of baby or just to check fetus’s development.

2. Minimize total exposure time. Duration of exposure time should be less than 40 minutes. Remember to choose a skilled or experienced operator.

3. Avoid Doppler, 3D, or 4D if possible unless there is a medical reason to use it.